EG H166 Hands-on Lab

Lab 8: Dimensions and Tolerances

 

 

Introduction ††††††††††††††††††††††††††††††

Background

Absolutely anything that is produced as a result of an engineer has some important dimensional characteristics. A chemical engineer must understand the angles made by chemical bonds and the atomic spacing in crystalline lattice structures.A machine designer must understand the clearances and displacement of moving parts, and determine the necessary size and shape of the machine's parts.A civil engineer measures the grade and width of roads and depth of stone fill and asphalt.

 

Every type of engineer uses measurement instruments, from a tape measure to electron microscopes, depending on which is best suited to the task.Knowing which type of instrument to use for a particular measurement must start from a knowledge of which types of instruments exist.

 

Purpose

The purpose of this lab is to familiarize you with feature inspection and product layout, tolerances, and to perform measurements and dimensions of parts provided.

Basic Principles

In this lab write-up, we will cover some basic principles behind:

1.      Importance of Dimensions to Manufacturing,

2.      Measurement Instruments, and

3.      Computer Usage for Measurement.

Lab Experience

The lab experience will encompass:

1.      Product Inspection, and

2.      Measurement.

 

 

 

 

Importance of Dimensions to Manufacturing

Dimensions

Dimensions are important in many areas of manufacturing.The assembly process requires that parts fit together as expected; if parts do not fit then they are rejected.Interchangeability is a vital requirement for every high volume manufacturing operation.Assembly is just one operation that specifies tolerances for the production of parts (how far off from the nominal dimension can a part be).Product usefulness is another factor in part tolerances.Consider a squirt gun that may be assembled properly, but always leaks.This product has a part or parts that were not made accurately enough to form a good seal.

 

Tolerances

Placing tolerances on dimensions must be done with a knowledge of the production process, as well as the end use of the product.Safety is another important factor in dimensional design and tolerances.Amusement park rides must be safe, even for people that enjoy risking their safety.Consider a roller coaster with a tunnel; what would happen if the tunnel height was set to be just one foot above a tall mans head?If anyone was brave and rode the roller coaster with their arms up (as many people do) then they could be seriously injured. The design of the product must understand the end use of the product.

 

Serviceability

Serviceability is another important factor for design of complex products.A car oil should be changed every 3000 miles, and so the oil filter and oil pan should be easily accessible since they are often removed (often car manufacturers push the limits of accessibility).It would be absurd to require removal of the engine to change the oil, and so the method of service for a product influences the design process.

 

 

 

 

 

 

 

 

 

 

 

Measurement Instruments

Introduction

There are a wide variety of measurement instruments, each one best suited for a particular style of measurement.Selecting the correct instrument is a talent that develops through experience.The two standard precision instruments are the micrometer and the dial caliper.Micrometers are typically used for outside dimensions up to just one inch, with precision to the 10,000th of an inch.Dial calipers are accurate to a 1,000th of an inch and can easily measure inside, outside and depth dimensions typically up to 6 inches.Dial calipers are the most versatile precision instruments.Other common dimensional instruments are tape measures, rulers, dial height gages, depth gages, wire gages, gap gages and angle gages.

 

 

Details of the Micrometer and Dial Caliper

The pages appended to this lab describe the use and function of a micrometer and a dial caliper

 

Computer Usage for Measurement

Coordinate Measurement Machine

Computers are becoming an important tool for almost every job imaginable.Measurement data can be acquired with data acquisition systems using a variety of positional measurement sensors and transducers; additionally computers can be utilized for detailed analysis and presentation of data through spreadsheets or more complex packages.

 

A computer-controlled machine is a coordinate measurement machine (CMM), which is dedicated to dimensional measurement. It can be programmed to automatically measure certain dimensions and contours of a part.CMMs are often used for quality control; by inspecting one part of a batch, the manufacturing process can be monitored and when parts start to exceed acceptable tolerances corrections can be made.

 

 

LAB EXPERIENCE

 

Make sketches of equipment used in class; include them in your lab write-up.

 
Product Inspection

Part Feature Inspection and Product Layout. Tolerances

 

1)            Disassemble the product provided and inspect the parts to determine which features are critical to the assembly operation. Analyze functionality of the product.

2)            Name, list and sketch each of the parts for the product.Be sure to indicate quantity for repeated parts.

3)            Produce neat sketches of the various parts indicating which features are important to assembly and functionality of the product.Provide sufficient detail to demonstrate your reasoning.

4)            Indicate the acceptable tolerances you determined were required for: a) assembly, and b) functionality with reference to your teamís sketches.

5)            Produce a neatly drawn exploded view sketch of the product with both dimensions and tolerances.

 

Measurement
 

1)            Measure and dimension the parts provided. Include a multi-view drawing of each part. These include cylinders, angle blocks, T-blocks, and a disk from a hard disk. Use the appropriate measuring tools for making the measurements. Each team will have a measurement toolkit that includes a micrometer, a caliper, a scale and a wire gage. An angle gage and a height gage must be shared.

2)            Each team member should measure the thickness of the disk from a hard disk using first a scale, then a caliper, and finally, a micrometer. Record each measurement and compare precision of the measuring devices.

3)            Use a wire gage to measure the diameter of the wire samples provided. Determine wire numbers (wire lengths are not required).

 

 

LAB REPORT

Format

   Lab reports must be done as a Team lab report.

   Follow given lab report format.

   Maximum 4-5 pages (including figures and tables)

 

General Guidelines

1.      Include a brief description of the lab

2.      Follow the lab experience as given in the lab write-up

3.      Answer the questions in the order given. Make and show sketches using drawing techniques. Use of CadKey is not required but is still an option.